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Basics and Current Implementations of Ultrasound Imaging of Shear Wave

Speed and Elasticity

Shigao Chen, PhD

Mayo Clinic College of Medicine

August 2016

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Disclosures

• Some technologies described here have been licensed. Mayo and Dr. Chen have financial interests in the technologies.

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Outline

• Significance and principle• Generation of shear waves• Detection of shear waves • Shear wave speed calculation• Sources of bias and variation

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1. Background and Principle of Elastography

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Why Tissue Stiffness?

THE BOOK OF PROGNOSTICS:“… Such swellings as are soft, free from pain, and yield to the finger, …and are less dangerous than the others.…then, as are painful, hard, and large, indicate danger of speedy death…”

Hippocrates, 400 B.C. 5©2014 MFMER | slide-6

Inherent Contrast

Ultrasound in Medicine & Biology 24(9): 1419-1435, 1998

• Limitations of palpation: subjective; small/deep lesions

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Ultrasound Elastography

US Elastography

Strain elastography

Shear wave elastography

• Qualitative and Indirect• Operator-dependent• Insufficient for diffuse diseases

• Quantitative and direct• Higher repeatability

2sc

Shear modulus Density (1000 kg/m3)

Shear wave speed

Ultrasound Transducer

kPa0

5

10

15

20

25

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2. Generation of Shear Waves

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A. External Vibration: Fibroscan

Shear Stiffness: μ = c2ρ

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Image courtesy of

Dr. Meng Yin.

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B. Single Push BeamUltrasound Transducer

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Amplitude of Shear Waves by a Push Beam

10 15 20 25 30 35 400

2

4

6

8

x (mm)

Dm

ax(

m)

• Increase push amplitude: Mechanical Index• Increase push duration: heating

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C. Supersonic Shear Imaging

www.supersonicimagine.com; Bercoff et al., 2004 12

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D. Comb-pushUltrasound Transducer

Comb-push

x (mm)S

low

tim

e (m

s)

5 10 15 20 25 30 35

5

10

15

20

25

Frequency (Hz)

Wav

e N

um

ber

(m

-1)

-500 0 500-500

0

500

2D FFT

Manduca et al., 2003 Deffieux et al., 2011

x (mm)

Slo

w t

ime

(ms)

5 10 15 20 25 30 35

5

10

15

20

25

x (mm)

Slo

w t

ime

(ms)

5 10 15 20 25 30 35

5

10

15

20

25

Directional Filter

x

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Comb-push (cont’d)Ultrasound Transducer

∆t

∆d

s

dc

t

2sc

Song et al., IEEE TMI 201214

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Heterogeneous Medium

x (mm)

z (m

m)

10 20 30

10

20

30

40

50

x (mm)

z (m

m)

10 20 30

10

20

30

40

50

m/s0

1

2

3

4

5

x (mm)

10 20 30

10

20

30

40

50

m/s0

1

2

3

4

5

x (mm)

z (m

m)

10 20 30

10

20

30

40

50

m/s0

1

2

3

4

5

Song et al., IEEE TMI, 201215

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3. Detection of Shear Waves

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Plane wave imager vs. Line-by-line scanner

Plane wave imager Line-by-line scanner

d

Frame rate = /

d = 4cm -> Frame rate ≈ 20 kHz

Frame rate = ∗ /

d = 4cm, N = 128-> Frame rate ≈ 150 Hz

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Plane wave imager

d

Frame rate = /

d = 4cm -> Frame rate ≈ 20 kHz

Line-by-line scanner

Frame rate = ∗ /

d = 4cm, N = 128, PB = 4-> Frame rate ≈ 600 Hz

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Plane wave imager vs. Line-by-line scanner

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Challenge in Shear Wave Detection

Plane wave imagers

Research platform

Less than 10% market

Line-by-line scanners

more than 90% of market

Clinical scanner

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Time Aligned Sequential Tracking (TAST)

Transducer

1 2 3 4 5

Vectors

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Data Alignment

•••

True data sample

Interpolated data sample

Data tracking trajectory

Aligned data points

Truncated data points

Tim

e

Vector 1

Vector 2

Vector 3

Vector 4

Vector 5

Lateral dimension

TAST

•••

•••

•••

•••

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GE LOGIQ E9 (LE9) with CUSELE9

SSI

Diam. (mm) 16.7 10.4 6.5 4.1 2.5

LE9 (kPa) 84.7 74.7 60.1 46.6 33.7

SSI (kPa) 87.3 73.2 61.6 42.5 32.1

Song et al., IEEE UFFC 201422

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Breast cancer study

Song et al., IEEE UFFC, 2014

Invasive mammary carcinoma Nottingham grade III of III

Normal

LE9 SSI

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4. Shear Wave Speed Calculation

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A. Time-to-Peak (TTP)

softstiff

C = inverse slope

Image courtesy of Dr. Kathy Nightingale

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B. Random Sample Consensus (RANSAC)

C=inverse slope

=c2

Image courtesy of Dr. Kathy Nightingale

Wang MH et al. Ultrasound Medicine and Biology, 36(5): 802-813, 2010.

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C. Cross CorrelationUltrasound Transducer

∆t

∆d

s

dc

t

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5.Sources of Bias

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A. Tissue Viscosity

29• Frequency of shear wave: push duration, f number…

2sc

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2211

22

2212

sc

Voigt model

0 200 400 6000

1

2

3

1 = 0.8 kPa, 2 = 0.8 Pa*s

Shear wave speed (m/s)

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B. Compression

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Barr et. al. Journal of Ultrasound in Medicine 31:895, 2012

• Probe compression, perfusion pressure

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C. Shear Wave Reflections

31Deffieus et. al. IEEE Trans. UFFC, 58:2032, 2011

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Summary

• Significance and principle• Generation of shear waves:

mechanical, single beam, Supersonic, Comb

• Detection of shear waves: TAST• Shear wave speed calculation:

Time to peak, RANSAC, correlation• Sources of bias and variation:

viscosity, compression, boundary32

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